Shigeyuki Komura

Adsorption of Janus particles to curved interfaces

We investigate the adsorption of a spherical Janus particle to a spherically curved liquid-liquid interface. We show that the equilibrium contact angle is determined by the geometry of the particle, its wettability, and also the interfacial curvature. In contrast with a homogeneous particle, there is a preferred interfacial curvature (spontaneous curvature) due to the Janus particle when the particle satisfies certain conditions.

Neutron spin–echo investigations of membrane undulations in complex fluids involving amphiphiles

Abstract The intermediate functions I ( Q , t ) obtained from neutron spin–echo (NSE) experiments were well fitted to I(Q,t)=I(Q,0) exp [−(Γt) 2/3 ] for the bicontinuous microemulsion and the lamellar phases of the C 12 E 5 / n -octane/water system and also for the lamellar phase of the DPPC/water/CaCl 2 system. The relaxation rate Γ increased as Q 3 . These results support the theory presented by Zilman and Granek [Phys. Rev. Lett. 77 (1996) 4788]. Bending modulus of the membrane ϰ was estimated in the C 12 E 5 / n -octane/water system and in the DPPC/water/CaCl 2 system using their theory.

Adsorption of colloidal particles to curved interfaces

As a simple model for a Pickering emulsion droplet, we consider the adsorption of spherical particles to a spherical liquid-liquid interface in order to investigate the curvature effect on the particle adsorption. By taking into account both the surface and the volume energies due to the presence of a particle, we show that the equilibrium contact angle is determined by the classical Youngs equation although the adsorption energy depends on the curvature. We also calculate the partitioning of the colloidal particles among the two liquids and the interface. The distribution of colloidal particles is expressed in terms of the interfacial curvature as well as the relative wettability of the particle.

Physical aspects of heterogeneities in multi-component lipid membranes.

Ever since the raft model for biomembranes has been proposed, the traditional view of biomembranes based on the fluid-mosaic model has been altered. In the raft model, dynamical heterogeneities in multi-component lipid bilayers play an essential role. Focusing on the lateral phase separation of biomembranes and vesicles, we review some of the most relevant research conducted over the last decade. We mainly refer to those experimental works that are based on physical chemistry approach, and to theoretical explanations given in terms of soft matter physics. In the first part, we describe the phase behavior and the conformation of multi-component lipid bilayers. After formulating the hydrodynamics of fluid membranes in the presence of the surrounding solvent, we discuss the domain growth-law and decay rate of concentration fluctuations. Finally, we review several attempts to describe membrane rafts as two-dimensional microemulsion.

Effects of an embedding bulk fluid on phase separation dynamics in a thin liquid film

Using dissipative-particle-dynamics simulations, we study the effects of an embedding bulk fluid on the phase separation dynamics in a thin planar liquid film. The domain growth exponent is altered from 2D to 3D behavior upon the addition of a bulk fluid, even though the phase separation occurs in 2D geometry. Correlated diffusion measurements in the film show that the presence of bulk fluid changes the nature of the longitudinal coupling diffusion coefficient from logarithmic to algebraic dependence of 1/s, where s is the distance between the two particles. This result, along with the scaling exponents, suggests that the phase separation takes place through the Brownian coagulation process.

Concentration fluctuations and phase transitions in coupled modulated bilayers.

We consider the formation of finite-size domains in lipid bilayers consisting of saturated and hybrid lipids. First, we describe a monolayer model that includes a coupling between a compositional scalar field and a two-dimensional vectorial order parameter. Such a coupling yields an effective two-dimensional microemulsion free energy for the lipid monolayer, and its characteristic length of compositional modulations can be considered as the origin of finite-size domains in biological membranes. Next, we consider a coupled bilayer composed of two modulated monolayers and discuss the static and dynamic properties of concentration fluctuations above the transition temperature. We also investigate the micro-phase separation below the transition temperature and compare the micro-phase separated structures with statics and dynamics of concentration fluctuations above the transition.

Non-linear rheology of lamellar liquid crystals

Abstract.We measure the non-linear relation between the shear stress and shear rate in the lyotropic lamellar phase of C12E5 /water system. The measured shear thinning exponent changes with the surfactant concentration. A simple rheology theory of a lamellar or smectic phase is proposed with a prediction

Mesoscale structures in microemulsions

\dot{{\gamma}}

Concentration fluctuations in binary fluid membranes

∼ σ3/2 , where

High- and Low-Pitch Helical Structures of Tilted Chiral Lipid Bilayers

\dot{{\gamma}}